1. Technical Field
This invention is related to a method of preventing the formation of carbonaceous deposits on engine components with the use of an amorphous hydrogenated carbon coating thereon.
2. Description of the Related Arts
Coking or the growth of hard carbonaceous deposits on components near or within the combustion chamber of internal combustion engines has been a long-standing problem. The buildup of deposits in this region can alter engine performance by impairing fuel economy, regulated emissions, and driveability, and in the worst case scenario cause engine damage. A detailed account of such deposits, problems and some attempted solutions can be found in S.A.E. Technical Paper No. 902105 (1990) by G. T. Kalghatgi. Carbonaceous deposits are especially problematic for fuel injectors located within the engine combustion chamber. Direct injection spark ignition (DISI) engines include a fuel injector injecting fuel directly into the combustion chamber.
Keeping the fuel injector free of carbonaceous deposits is important to the efficient and regulated operation of the engine. The fuel injector determines the fuel spray pattern. The fuel injector tips project into the cylinders and operate at high pressure and temperature. The fuel injector is constantly exposed to combustion gas and fuel. It was found that carbonaceous deposits build in a volcano shape around the orifice on the face plate of the injector. By partially blocking the orifice, the deposits reduce fuel flow and change the fuel spray pattern. This results in unstable and uncontrolled fuel mixing and delivery as well as combustion that causes engine knock, decreased fuel economy and increased emissions. While there are several methods to reduce the carbonaceous deposits including improved fuel injector design, and adding dispersion and detergents to the fuel, these alternative methods are insufficient and still allow for the unwanted carbonaceous deposits.
If the fuel injector could be made to resist the carbonaceous deposits, existing fuels and fuel injector designs could be utilized. In the past, components have been coated with amorphous hydrogenated carbon to increase hardness and durability, decrease friction and wear and protect against corrosion. As described in U.S. Pat. Nos. 5,249,554, 5,309,874, and 5,237,967 assigned to Ford Motor Company, and incorporated herein by reference, power train components have been coated with such carbon film coatings to reduce friction and wear related thereto. More recently, coatings have also been applied in an effort to reduce deposit formation. One example is U.S. Pat. No. 3,552,370, issued to Briggs et al, which describes a coating, and method of application, including the constituents of nickel, aluminum and copper for the purpose of reducing heat transfer from the combustion chamber to foster a more complete combustion. In the Briggs patent, a thermal mechanism is utilized preventing deposits. Under this thermal approach, the higher temperature of the coated component promotes combustion rather than deposit of hydrocarbon species. If the coating is used inside the combustion chamber, however, care must be taken with this approach so that the coated surface does not heat to an excessive temperature. If this occurs, the excessively hot coating itself might cause premature combustion. Accordingly, for the prevention of carbonaceous deposits near or in the proximity of the combustion chamber, deposit prevention using a thermal mechanism has significant limitations. Another approach for preventing deposits is a chemical method. Under this approach, a coating is supplied by which the precursor molecules for forming a deposit cannot chemically bond to the surface. An example of this approach is a Teflon.TM. coating.
However, Teflon.TM. coatings, in particular, are unsuited for application on many engine components due to the high temperature and high hardness properties required for use in an internal combustion engine. In the case of the injector face plate, the former is the reason for unsuitability.
U.S. Pat. No. 5,771,873, which is commonly assigned, teaches a method of using SiFl.sub.4 precursor gases to form a deposit resistant coating. The U.S. Pat. No. 5,771,873 included coatings that also were wear resistant as well as deposit resistant. The present invention has further developed these coatings and has identified F-AHC coatings that are particularly well suited to resist carbonaceous deposits on a fuel injector where wear properties are not as important.
There thus remains a need for a method of reducing and preventing the growth of carbonaceous deposits on fuel injectors.